I bought 20 of these to use in my third grade classroom. So far, they're working great. The students love them and they're holding air well. When you first blow them up, you have to bounce on them a little bit and unstopper them and pump more air in to get them blown up all the way. It isn't a flaw with the ball -- all yoga/stability balls are like this. If you don't do this, they will seem a little small. But the material is thicker than I expected. Honestly, for $6 each, these are a complete steal and I recommended them to all the teachers in my building.